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Add ip6tables rule for DHCPv6 hop limit configuration #865

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Merged
sknat merged 1 commit into from
Jan 30, 2026
Merged

Add ip6tables rule for DHCPv6 hop limit configuration #865

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2 changes: 1 addition & 1 deletion vpp-manager/images/ubuntu/Dockerfile
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ RUN apt-get update \
&& apt-get install -y openssl libapr1 libnuma1 \
libmbedcrypto7 libmbedtls14 libmbedx509-1 libsubunit0 \
iproute2 ifupdown ethtool libnl-3-dev libnl-route-3-dev \
libpcap0.8 libunwind8 \
libpcap0.8 libunwind8 iptables \
gdb \
&& rm -rf /var/lib/apt/lists/*

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48 changes: 48 additions & 0 deletions vpp-manager/vpp_runner.go
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Original file line number Diff line number Diff line change
Expand Up @@ -864,6 +864,46 @@ func (v *VppRunner) AllocatePhysicalNetworkVRFs(phyNet string) (err error) {
return nil
}

func (v *VppRunner) configureDHCPv6HopLimit() {
log.Infof("Configuring ip6tables mangle OUTPUT rule for DHCPv6 hop limit on host")

checkCmd := exec.Command("/usr/sbin/ip6tables", "-t", "mangle", "-C", "OUTPUT",
"-p", "udp", "--sport", "546", "--dport", "547",
"-j", "HL", "--hl-set", "2")
if err := checkCmd.Run(); err != nil {
outputCmd := exec.Command("/usr/sbin/ip6tables", "-t", "mangle", "-A", "OUTPUT",
"-p", "udp", "--sport", "546", "--dport", "547",
"-j", "HL", "--hl-set", "2")
outputCmd.Stdout = os.Stdout
outputCmd.Stderr = os.Stderr
if err := outputCmd.Run(); err != nil {
log.Warnf("Failed to configure ip6tables mangle OUTPUT rule for DHCPv6: %v", err)
}
} else {
log.Infof("ip6tables mangle OUTPUT rule for DHCPv6 already present")
}
}

func (v *VppRunner) cleanupDHCPv6HopLimit() {
log.Infof("Cleaning up ip6tables mangle OUTPUT rule for DHCPv6 hop limit on host")

checkCmd := exec.Command("/usr/sbin/ip6tables", "-t", "mangle", "-C", "OUTPUT",
"-p", "udp", "--sport", "546", "--dport", "547",
"-j", "HL", "--hl-set", "2")
if err := checkCmd.Run(); err == nil {
deleteCmd := exec.Command("/usr/sbin/ip6tables", "-t", "mangle", "-D", "OUTPUT",
"-p", "udp", "--sport", "546", "--dport", "547",
"-j", "HL", "--hl-set", "2")
deleteCmd.Stdout = os.Stdout
deleteCmd.Stderr = os.Stderr
if err := deleteCmd.Run(); err != nil {
log.Warnf("Failed to delete ip6tables mangle OUTPUT rule for DHCPv6: %v", err)
}
} else {
log.Infof("ip6tables mangle OUTPUT rule for DHCPv6 not present")
}
}

// Returns VPP exit code
func (v *VppRunner) runVpp() (err error) {
if !v.allInterfacesPhysical() { // use separate net namespace because linux deletes these interfaces when ns is deleted
Expand Down Expand Up @@ -936,6 +976,13 @@ func (v *VppRunner) runVpp() (err error) {
return errors.Wrap(err, "Error configuring VPP")
}

// FIXME This is a temporary workaround using ip6tables to set the hop limit for DHCPv6.
// Ideally, VPP should have a dedicated node for handling this.
// Without this, when forwarding a DHCPv6 SOLICIT/REQUEST packet, VPP will decrement the
// hop-limit by 1. Since client generates DHCPv6 SOLICIT/REQUEST with hop-limit=1, VPP
// drops it (ip6 ttl <= 1) with ICMP time exceeded and DHCPv6 lease negotiation fails.
v.configureDHCPv6HopLimit()

// add main network that has the default VRF
config.Info.PhysicalNets[config.DefaultPhysicalNetworkName] = config.PhysicalNetwork{VrfID: common.DefaultVRFIndex, PodVrfID: common.PodVRFIndex}

Expand Down Expand Up @@ -1001,6 +1048,7 @@ func (v *VppRunner) runVpp() (err error) {

func (v *VppRunner) restoreConfiguration(allInterfacesPhysical bool) {
log.Infof("Restoring configuration")
v.cleanupDHCPv6HopLimit()
err := utils.ClearVppManagerFiles()
if err != nil {
log.Errorf("Error clearing vpp manager files: %v", err)
Expand Down
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